The present invention relates to a method for manufacturing a semiconductor device. The present invention also relates to a method for manufacturing a microphone having an acoustic sensor mounted in a package.
(General Microphone)
FIG. 1 is a cross-sectional view of a conventional microphone having a general structure. A microphone 11 has an acoustic sensor 15 and a signal processing circuit 17 mounted in a package formed from a cover 12 and a circuit board 13. The acoustic sensor 15 and the signal processing circuit 17 are mounted being arranged side by side on the upper surface of the circuit board 13. The signal processing circuit 17 is covered by sealing resin 21. The acoustic sensor 15 and the signal processing circuit 17 are electrically connected by a bonding wire 18, and the signal processing circuit 17 is further connected to a board wiring 14 of the circuit board 13 by a bonding wire 19.
Normally, the lower surface of the circuit board 13 is mounted on a printed wiring board, and is adhered to the printed wiring board. Accordingly, a sound introduction hole 20 for introducing acoustic vibration into the package is opened in the upper surface of the cover 12. The lower surface of the acoustic sensor 15 is bonded to the circuit board 13, and the lower surface of a back chamber 16 is blocked by the circuit board 13.
In a capacitance microphone, there is a correlation between the sensitivity of the microphone and the capacity of the back chamber, and the sensitivity of the microphone decreases as the capacity of the back chamber decreases. In the microphone 11, since the sound introduction hole 20 is provided to the cover 12, and the space between the acoustic sensor 15 and the circuit board 13 forms the back chamber 16, the capacity of the back chamber 16 cannot be increased, and it is difficult to improve the sensitivity of the microphone 11.
(Microphone of Patent Document 1)
A microphone disclosed in Patent Document 1 (JP 2007-178221 A) is shown in FIG. 2. In a microphone 31 of Patent Document 1, the signal processing circuit 17 is mounted on the upper surface of the circuit board 13. A spacer 32 is fixed to the upper surface of the circuit board 13, at a position adjacent to the signal processing circuit 17, and the acoustic sensor 15 is further mounted on the upper surface of the spacer 32. A vertically penetrating through-hole 33 is opened in the spacer 32. An electrode pad is provided to the lower surface of the acoustic sensor 15, and the acoustic sensor 15 is electrically connected to the circuit board 13 via the spacer 32. The sound introduction hole 20 is opened in the cover 12.
In the microphone 31, the through-hole 33 of the spacer 32 is continuous with the back chamber 16 of the acoustic sensor 15, and thus, the space below a diaphragm is widened. As a result, the capacity of the back chamber 16 of the acoustic sensor 15 can be substantially increased, and the sensitivity of the microphone 31 is improved.
However, according to such a structure, since the spacer 32 is mounted on the upper surface of the circuit board 13, and the acoustic sensor 15 is further mounted on the spacer 32, there is an inconvenience that the height of the microphone 31 is great.
As a method for reducing the height of such a microphone, there is conceivable a method for reducing the height of the acoustic sensor by polishing and thinning the substrate portion of the acoustic sensor in the manufacturing process of the acoustic sensor. However, in the manufacturing process of the acoustic sensor, a plurality of acoustic sensors is fabricated at one time on a wafer. Accordingly, if the substrate portion of the acoustic sensor is to be made thin, the wafer is to be polished and thinned during the manufacturing process of the acoustic sensor.
As the wafer, a thin wafer with a large diameter is usually used. Accordingly, if the wafer is polished and made even thinner, rigidity of the wafer is greatly reduced. As a result, the wafer may be cracked or chipped in the polishing process or a subsequent process, and a yield of the acoustic sensor may be reduced.
The present invention has been devised to solve the problems described above, and an object thereof is to provide a method for manufacturing a semiconductor device structured to have a semiconductor element mounted on a support member (for example, a microphone structured to have an acoustic sensor mounted on a support member), the method being capable of reducing the height of the semiconductor element, and thereby reducing the height of the semiconductor device.